The translation of unparalleled efficiency from the lab-scale devices to practical-scale flexible modules affords a huge performance loss for flexible perovskite solar cells (PSCs). The degradation ...is attributed to the brittleness and discrepancy of perovskite crystal growth upon different substrates. Inspired by robust crystallization and flexible structure of vertebrae, herein, we employ a conductive and glued polymer between indium tin oxide and perovskite layers, which simultaneously facilitates oriented crystallization of perovskite and sticks the devices. With the results of experimental characterizations and theoretical simulations, this bionic interface layer accurately controls the crystallization and acts as an adhesive. The flexible PSCs achieve the power conversion efficiencies of 19.87% and 17.55% at effective areas of 1.01 cm
and 31.20 cm
respectively, retaining over 85% of original efficiency after 7000 narrow bending cycles with negligible angular dependence. Finally, the modules are assembled into a wearable solar-power source, enabling the upscaling of flexible electronics.
As a new generation of solid-state film cells, organic solar cells (OSCs) have become the research focus in the field of renewable energy sources, and the reported power conversion efficiencies ...(PCEs) have been boosted to 18%. Hole transport layer (HTL) materials, a critical component of OSCs, exert a tremendous impact on the PCE and stability of OSCs. At present, the HTL materials used in OSCs can be divided into two main categories, which are inorganic HTL materials and organic HTL materials. Although, OSCs with inorganic HTL materials can achieve satisfactory PCE, they are not suitable for large-scale commercial roll-to-roll production due to the unavoidable process of high-temperature vacuum evaporation. Recently, a great number of organic HTL materials have been designed, synthesized, and successfully applied in OSCs. Herein, we review the recent advances in organic HTL materials in single-junction OSCs and systematically discuss the relationships between the structure and properties of various HTL materials, and highlight the design rules of HTL materials for highly efficient and stable OSCs.
The hole transport layer plays a crucial role in enhancing the PCE and stability of OSCs.
The flexibility of organic photovoltaics (OPVs) has attracted worldwide attention in recent years. To realize the bending-stability of OPVs, it is necessary to put forward the bending-stability of ...interfacial layer. A novel bendable composite is explored and successfully applied as an electron transport layer (ETL) for fully-flexible OPVs. We incorporated poly(vinylpyrrolidone)(PVP) into conjugated electrolytes (CPE) to composite a bendable ETL for high-performance OPVs devices. Fortunately, the devices based on PVP-modified CPE exhibited better device performances and more excellent mechanical properties of bendability. The fullerene-free OPVs based on PM6:IT-4F with CPE@PVP as ETLs yield the best power conversion efficiency (PCE) of 13.42%. Moreover, a satisfying efficiency of 12.59% has been obtained for the fully-flexible OPVs. As far as we know, this is one of the highest PCE for fully-flexible OPV based PM6:IT-4F system. More importantly, the flexible OPVs devices can retain more than 80% of its initial efficiency after 5000 bending cycles. Furthermore, among various curvature radii, the mechanical properties of the device based on CPE@PVP are superior to those of the device based on bare CPE as ETL. These findings indicate that the functional flexibility of CPE as a cathode interfacial layer is an effective strategy to fabricate high-performance flexible devices in the near future.
The fluorobenzotriazole (FTAZ)‐based copolymer donors are promising candidates for nonfullerene polymer solar cells (PSCs), but suffer from relatively low photovoltaic performance due to their ...unsuitable energy levels and unfavorable morphology. Herein, three polymer donors, L24, L68, and L810, based on a chlorinated‐thienyl benzodithiophene (BDT‐2Cl) unit and FTAZ with different branched alkyl side chain, are synthesized. Incorporation of a chlorine (Cl) atom into the BDT unit is found to distinctly optimize the molecular planarity, energy levels, and improve the polymerization activity. Impressively, subtle side chain length of FTAZ realizes a dramatic improvement in all the device parameters, as revealed by the short‐current density (Jsc) improved from 7.41 to 20.76 mA cm−2, fill‐factor from 36.3 to 73.5%, and even the open‐circuit voltage (Voc) from 0.495 to 0.790 V. The best power conversion efficiency (PCE) of 12.1% is obtained from the L810‐based device, which is one of the highest values reported for FTAZ‐based PSCs so far. Notably, the corresponding external quantum efficiency curve keeps a very prominent value up to 80% from 500 to 800 nm. The notable performance is discovered from the reduced energy loss, improved molecular face‐on orientation, the down‐shifted energy levels, and optimized absorption coefficient regulated by side‐chain engineering.
Three polymers L24, L68, and L810 are developed as donor materials for organic solar cells. As the alkyl side chain of the fluorobenzotriazole (FTAZ) unit increases, the L810‐based device exhibits lower energy loss, better molecular face‐on orientation, and a higher absorption coefficient. Consequently, the power conversion efficiency is improved to 12.1%, which is one of the highest values for FTAZ‐based devices.
Highlights
Alkyl-tailored Y-SMAs named YR-SeNF series with near-infrared absorption, different molecular crystallinity and self-assembly abilities are developed.
The related organic solar cells ...(OSCs) with an active layer processed from halogen-free solvents and spin-coating-free technologies achieve a ~ 19% efficiency.
Ternary OSCs offer a robust operating stability under MPP tracking and well-keep > 80% of the initial efficiency for even over 400 h.
Power-conversion-efficiencies (PCEs) of organic solar cells (OSCs) in laboratory, normally processed by spin-coating technology with toxic halogenated solvents, have reached over 19%. However, there is usually a marked PCE drop when the blade-coating and/or green-solvents toward large-scale printing are used instead, which hampers the practical development of OSCs. Here, a new series of
N
-alkyl-tailored small molecule acceptors named YR-SeNF with a same molecular main backbone are developed by combining selenium-fused central-core and naphthalene-fused end-group. Thanks to the
N
-alkyl engineering, NIR-absorbing YR-SeNF series show different crystallinity, packing patterns, and miscibility with polymeric donor. The studies exhibit that the molecular packing, crystallinity, and vertical distribution of active layer morphologies are well optimized by introducing newly designed guest acceptor associated with tailored
N
-alkyl chains, providing the improved charge transfer dynamics and stability for the PM6:L8-BO:YR-SeNF-based OSCs. As a result, a record-high PCE approaching 19% is achieved in the blade-coating OSCs fabricated from a green-solvent
o
-xylene with high-boiling point. Notably, ternary OSCs offer robust operating stability under maximum-power-point tracking and well-keep > 80% of the initial PCEs for even over 400 h. Our alkyl-tailored guest acceptor strategy provides a unique approach to develop green-solvent and blade-coating processed high-efficiency and operating stable OSCs, which paves a way for industrial development.
All-polymer solar cells (all-PSCs) have attracted enormous attention and achieved significant progress in recent years due to their long-term stability and excellent film stretchability. However, the ...problem of morphology control in bulk-heterojunction (BHJ) films due to highly entangled polymeric chains hinders the further improvement of device performance. In this work, we obtained fine-tuned photoactive layer morphology through reconstructed microstructure induced by steric effects to realize an improved device performance in ternary all-PSCs. The large tetrahexylphenyl substituents on the backbone of naphthalene diimide–indacenodithienothiophene based copolymer acceptor BL-102 bring forth the steric-hindrance effect and influence intermolecular interactions. Therefore, the copolymer BL-102 delivers the property of suppressed self-aggregation, causing reconstructed crystalline features and morphology in blending films. The ternary devices tended to reduce the excessive phase separation by suppressing the aggregation of original polymers but to promote intermixing behaviors. Therefore, the optimal BHJ film manifested a well-formed bi-continuous interpenetrating nanoscale network with a larger π–π stacking coherence length and ordered face-on molecular orientation. Hence, a faster electron transfer (ET) and hole transfer (HT) process combined with balanced charge carrier mobilities can be achieved to enhance the overall device performance. This work provides an effective method to regulate the photoactive layer morphology of all-PSCs through structurally steric hindrance effects and demonstrate the significance of ternary-blending strategy induced nanoscale morphology modulation for fabricating highly efficient all-PSCs.
Fabricating ternary solar cells is a pivotal strategy to improve the power conversion efficiencies (PCEs) of organic photovoltaic devices. However, it is still a challenge to simultaneously improve ...the performance parameters of ternary devices. Therefore, the third ingredient in ternary blends should be precisely designed or selected. Herein, a new medium‐bandgap small‐molecule acceptor, namely, 3,9‐bis(2‐methylene‐(3‐(1‐(3,5‐dimethylphenyl)‐1cyanomethylene)indanone))‐5,5,11,11‐tetrakis‐(4‐hexylphenyl)dithieno2,3‐d:2′,3′‐d′‐sindaceno1,2‐b:5,6‐b′dithiophene (ITIF), is synthesized by end‐capping with a new fluorinated, asymmetric terminal group, (Z)‐2‐(3,5‐difluorophenyl)‐2‐(3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) acetonitrile. Replacing the CN substituent with the asymmetric 3,5‐difluorophenyl substituent obviously up‐shifts the lowest unoccupied molecular orbital (LUMO) level of ITIF to −3.78 eV, enlarges the bandgap to 1.82 eV, and improves the absorption coefficient to ≈50% higher than that of 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)indanone))‐5,5,11,11‐tetrakis‐(4‐hexylphenyl)dithieno2,3‐d:2′,3′‐d′‐sindaceno1,2‐b:5,6‐b′dithiophene (ITIC). Due to the similar structures, ITIF and ITIC can combine as an alloyed acceptor, which makes it convenient to tune the morphology and optical and electrochemical properties of ternary blends. The enhanced absorption coefficient of ITIF and the rapid fluorescence resonance energy transfer from ITIF to ITIC remarkably improve the absorption of the ternary blend film, hence compensating for the external quantum efficiency (EQE) curves. When ITIF is introduced into ternary solar cells based on poly(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo1,2‐b:4,5‐b′dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo1′,2′‐c:4′,5′‐c′dithiophene‐4,8‐dione) (PBDB‐T):ITIF:ITIC blends, the PCEs of the ternary devices are increased from 9.2% to 10.5%, and the short‐circuit currents, open‐circuit voltages, and fill factors are simultaneously improved.
A new asymmetric, terminally tetrafluorinated nonfullerene acceptor, namely ITIF, was prepared for ternary solar cells based on PBDB‐T:ITIF:ITIC blends. Owing to the unique structure, ITIF is promised to work efficiently in ternary blends, simultaneously boosting the devices performance parameters. Therefore, the power conversion efficiencies of the ternary solar cells are boosted from 9.2% to 10.5%.
The excited state charge transfer (CT) characteristics of nonfullerene acceptors play an important role in determining the photo excited CT mechanisms and performance for organic solar cells (OSCs). ...Here, we systematically investigated the structure–property relationship and excited state CT characteristics based on A–D–A and A–DA′D–A type acceptors by density functional theory (DFT) and time-dependent DFT (TD-DFT). Comparing to the A–D–A type acceptors IT-4F and DTPC-DFIC, the A–DA′D–A type acceptor Y6 exhibits distinct structural and electronic characteristics, such as featuring larger Mulliken electronegativity, molecular polarity index (MPI), and electrostatic potential (ESP). Besides this, the larger hole and electron delocalization index (HDI, EDI) proves more effective charge separation for Y6. Their excited state CT characteristics are all mainly from the intermediate cores to the terminal units, while the CT in the opposite direction of Y6 is stronger than that of IT-4F and DTPC-DFIC, which provides theoretical support for the formation of multielectron transport channels in 3D network structure. These results may explain why Y6 and its derivatives show such efficient photovoltaic performance and provide a theoretical basis for the design and screening of novel acceptors as well as further deepen the understanding of the excited states charge transfer in OSCs.
The precise design of organic photovoltaic materials and the control of morphology in the active layer are crucial for achieving high-performance organic solar cells (OSCs). However, it still remains ...difficult to fully obtain the intrinsic properties of organic photovoltaic materials, as well as the details of molecular stacking in disordered films and the evolution of the specific morphology of active layers, using traditional characterization methods, which hinders the screening of organic photovoltaic materials and understanding the structure-property relationship. Accordingly, computational chemistry provides a good method and plays a vital role in current scientific research. In this review, we first introduce the theoretical methods used in the recent study of OSCs, including density functional theory (DFT), time-dependent DFT (TD-DFT), all atomic molecular dynamics (AAMD) and coarse-grained molecular dynamics (CGMD). Then, the effects of the molecular structure on its conformation, frontier molecular orbital, ultraviolet-visible (UV-Vis) absorption spectrum, dipole moment, electrostatic potential, binding energy, stacking, and morphological evolution are discussed and analyzed. In addition, the application of machine learning (ML) in materials screening is briefly summarized. Finally, the intrinsic properties of OSCs are summarized based on the molecular structure and the future development and prospects of OSCs are analyzed to accelerate the efficiency over 20% in the near future.
This review summarizes the recent advances of computational chemistry in OSC research to provide a deeper insight into the relationship between molecular structure and photoelectrical properties.
Device engineering is an effective way to improve the photovoltaic performance of organic solar cells (OSCs). Currently, the widely used bulk heterojunction (BHJ) structure has problems such as ...material solubility limitations and the emerging pseudoplanar heterojunction (PPHJ) structure is also troubled by printing technology requirements. However, these issues can be solved by the reasonable application of traditional planar heterojunction (PHJ) structure. Herein, PM6:BO‐4F system is selected to prepare PHJ devices by combining sequential spin‐coating and orthogonal solvent strategy. In view of the good solubility of PM6 and BO‐4F in commonly used high‐boiling solvent chlorobenzene (CB) and green solvent tetrahydrofuran (THF), respectively, the PHJ devices are successfully prepared by using these two orthogonal solvents, achieving a power conversion efficiency (PCE) of 15.6%. On this basis, green nonhalogen reagent o‐xylene (O‐XY) is further used to process PM6. Due to the large polarity difference between O‐XY and THF, all‐green solvent‐processed PHJ devices are successfully fabricated and obtain an astonishing PCE of 16%. As far as it is known, it is the highest efficiency for PHJ OSCs. The results prove the huge research potential of PHJ structure and point out new direction for solving OSC materials compatibility, long‐term stability, and future commercial applications.
Device engineering is an effective way to improve the photovoltaic performance of organic solar cells. Herein, PM6:BO‐4F system is selected to prepare planar heterojunction (PHJ) devices. The PHJ devices are successfully fabricated by using green orthogonal solvents of o‐xylene (O‐XY) and tetrahydrofuran (THF), achieving an excellent power conversion efficiency (PCE) of 16%, which is the highest efficiency of the PHJ structure.
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